Add version api ref

Change-Id: I93cb484a1f3ae533558ecde0cd79c8b6b2fb18f1

api-ref/source/watcher-api-versions.inc

@@ -0,0 +1,81 @@
+.. -*- rst -*-
+
+============
+API versions
+============
+
+In order to bring new features to users over time, the Watcher API
+supports versioning. There are two kinds of versions in Watcher.
+
+- ''major versions'', which have dedicated URLs.
+- ''microversions'', which can be requested using the
+  ``OpenStack-API-Version`` header.
+
+.. note:: The maximum microversion depends on release.
+  Please reference:
+  `API Microversion History
+  <https://docs.openstack.org/watcher/latest/contributor/api_microversion_history.html>`__
+  for API microversion history details.
+
+The Version API resource works differently from other API resources as they *do not*
+require authentication.
+
+If Watcher receives a request with unsupported version, it responds with a 406 Not Acceptable,
+along with the -Min- and -Max- headers that it can support.
+
+List API versions
+=================
+
+.. rest_method::  GET /
+
+This fetches all the information about all known major API versions in the
+deployment. Links to more specific information will be provided for each major
+API version, as well as information about supported min and max microversions.
+
+Normal response codes: 200
+
+Request
+-------
+
+Response Example
+----------------
+
+.. rest_parameters::  parameters.yaml
+
+    - description: version_description
+    - versions: versions
+    - version: version
+    - id: version_id
+    - links: links
+    - min_version: openstack-api-min-version
+    - max_version: openstack-api-max-version
+
+.. literalinclude:: samples/api-root-response.json
+   :language: javascript
+
+
+Show v1 API
+===========
+
+.. rest_method::  GET /v1/
+
+Show all the resources within the Watcher v1 API.
+
+Normal response codes: 200
+
+Request
+-------
+
+Response Example
+----------------
+
+.. rest_parameters::  parameters.yaml
+
+    - id: version_id
+    - links: links
+    - OpenStack-API-Version: header_version
+    - OpenStack-API-Minimum-Version: openstack-api-min-version
+    - OpenStack-API-Maximum-Version: openstack-api-max-version
+
+.. literalinclude:: samples/api-v1-root-response.json
+   :language: javascript